1. Field of the Invention
This invention relates to a process for producing fluorine-containing organic compounds.
2. Description of the Prior Art
Compounds containing fluorine have versatile useful applications by virtue of their superior stability, chemical resistance, weather resistance, water and oil repellent properties, physiological activity and so on. A variety of studies have been made on the compounds containing the fluorine-containing alkyl group within their molecules, and several new synthesizing methods have been hitherto developed.
There are reported of the synthesizing methods; for the compounds containing trifluoromethyl group, the followings may be mentioned, (1) a method to directly fluorinate the methyl group with metallic fluorides, (2) an halogen exchange reaction on CCl.sub.3 group with HF-SbCl.sub.5, (3) a method to fluorinate COOH group with SF.sub.4, (4) radical reaction to introduce a CF.sub.3 group into heterocyclic compounds, (5) a method to substitute iodine which is introduced into aromatic compounds for Rf by means of RfCuI (Ullmann-type reaction) (Rf indicates fluorine-containing aliphatic group: hereinafter it is so represented).
Further, it is known that the trifluoromethyl magnesium iodide (CF.sub.3 MgI) can not be used for trifluoromethylation reaction in that the compound is very unstable due to its property to eliminate MgF.sub.2 by readily extracting F because its constituent Mg is highly bondable with F.
Among above-described synthesizing methods for trifluoromethyl-containing compounds, the methods other than the Ullmann-type reaction, the reagent for fluorination is highly hazardous, and that its handling is difficult, and that it is hard to optionally introduce the trifluoromethyl group into a desired position in a molecule.
Conversely, there is reported that .beta.-keto carboxylic acid ester can be synthesized by applying the Reformatsky reaction on ester compounds.
However, the reaction is difficult and less successful instances are known up to the present. The details are explained as follows:
Firstly, .alpha.-carboxylic acid ester (1) is caused to react with zinc in accordance with the following reaction, then a Reformatsky-type reagent (2). is obtained. ##STR1## In this case, it is undesirable when the raw material, ester (1) and the product, ester (2), are condensated, and ##STR2## is produced. Thus, it was a prerequisite to handle them without generating the above result (or preventing the reaction of both esters).
Accordingly, in obtaining an end product .beta.-ketocarboxylic acid ester (4) by subjecting the above-described reagent (2) to reaction with a ester compound (3) with the following formula, due to the above prerequisite, it becomes difficult to cause the reaction itself of the ester (2) with the ester (3). ##STR3## Thus, it is necessary to select an ester that may easily react with the reagent (2) without self-condensation between the ester (1) and (2).
This is a reason why there have been almost no successful experimental results in the synthesizing of the compound as intended.
In consequence, even when the fluorine-containing ester which is represented by R.sub.f COOR' (R.sub.f : fluorine-containing alkyl group is employed as the above-described ester compound (3) so as to introduce fluorine into the object compound, it is not easy to obtain a fluorine-containing alkyl keto carboxylic acid ester by means of the said Reformatsky reaction.